The alkaline-catalyzed/carbon dioxide bulk polymerization of 2-pyrrolidone with conversions of 30-40% or more, is known to produce a hard mass which, when chopped, washed and dried, is suitable for melt-spinning into fibers, or other processing (see U.S. Pat. No. 3,721,652). However, the continuous bulk polymerization of 2-pyrrolidone under agitation produces a finely comminuted product which is washed with water to remove both unreacted monomer and the alkaline catalyst. The polypyrrolidone product is then in the form of a wet powder containing about 50 weight percent water, based on polypyrrolidone. This powder is normally dried, but it has too low a bulk density for economical commercial processing, e.g., it is difficult to feed into an extruder for melt-spinning into filaments. Consequently, the dry powder is melt-extruded to form dense pellets which are suitable for feeding into extruders in melt-spinning processes. In the process of melt-extruding the polypyrrolidone to form dense pellets, its weight average molecular weight is degraded from a high initial value of about 200,000, or more, to a value of 35,000-100,000 or less, because of the well-known tendency of nylon-4 to decompose into its monomer upon melting. U.S. Pat. No. 3,814,792 uses an alcohol/water solvent at elevated temperature to dissolve a polypyrrolidone composition for extrusion. U.S. Pat. No. 3,686,066 discusses the molding of solid nylon-4 articles from water-swollen polypyrrolidone containing 100% or more of water, based on the weight of polypyrrolidone, by applying heat and pressure to the swollen mass. U.S. Pat. No. 3,324,061 teaches the use of elevated temperatures and pressures to dissolve polypyrrolidone in water for dry spinning. It is an object of the present invention to provide a means of increasing the bulk density of polypyrrolidone without substantially degrading its molecular weight.